1. Field of the Invention
The present invention relates to a display device capable of performing the functions of both a light-reflecting display and a light-emitting display, particularly, to a display device that permits achieving light-emitting display by utilizing an electrochemiluminescence or electrogenerated chemiluminescence (ECL) material performing an ECL display and also permits achieving light-reflecting display by utilizing an electrochromic (EC) material performing the EC display.
2. Description of the Related Art
A translucent liquid crystal display (LCD) device capable of performing both light-reflecting display and light-emitting display is proposed as a display for, for example, a mobile phone that is used outdoors and indoors. The translucent LCD is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 2003-241188. As shown in FIG. 3 and described on pages 3 to 5 of this patent document, a reflective layer having an irregular surface is formed in a part of the pixel for the reflective display for displaying the pixel by reflecting external light rays. Also, a transmitting display section is formed in the other region for the light-emitting display in which the transmittance of the light rays emitted from a back-light is controlled so as to cause the light rays to be directed outward. The back-light is arranged below the transmitting display section.
In the method outlined above, in which it is possible to achieve both the light-reflecting display and the light-emitting display, it is possible to achieve a sufficiently bright and clear display depending on the brightness of the back-light when it comes to the light-emitting display mode. However, when it comes to the light-reflecting display mode, a difficulty remains unsolved in terms of the capability of obtaining a clear display having a sufficiently high contrast because of the limitation in the principle of the display of the liquid crystal that a polarizing plate is used and the limitation in terms of the display area that a single pixel is divided into two regions consisting of a light-reflecting display region and a light-emitting display region.
In contrast, an electrochromic display (ECD) is known to the art as a display that permits a light-reflecting display having a high contrast. The particular display device is disclosed in, for example, Japanese Patent Disclosure No. 2003-21848. As described on pages 4 to 14 of this patent document with reference to FIG. 1, an electrochromic (EC) material and an electrolyte are arranged between two electrodes so as to form the particular display device. Incidentally, the electrochromic material noted above is a material whose properties are changed as a result of the electrochemical oxidation or reduction. Specifically, the color of the electrochromic material noted above is changed or the electrochromic material is precipitated or dissolved as a result of the electrochemical oxidation or reduction. However, a difficulty remains unsolved in the electrochromic display (ECD) in that the display is hard to see in the dark place because the electrochromic display (ECD) performs light-reflecting display alone.